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Inside USB 3.0

What makes SuperSpeed tick

NEC last week announced what it claims is the world's first host controller chip for USB 3.0 - aka SuperSpeed USB because of its 5Gb/s peak data-transfer rate.

Since the Universal Serial Bus isn't a peer-to-peer system - unlike Firewire, for instance - NEC's chip isn't enough to allow manufacturers to offer USB 3.0 peripherals yet, but once the part ships - it's due next month - they will be able to prepare SuperSpeed PC designs.

NEC reckons that after releasing small, 'sample' quantities of the chip in June, it'll ramp up production to significantly larger volumes in Q3, allowing computer makers to take those designs and put them on shop shelves. There may not be many - or even any - SuperSpeed peripherals to hook up to these machines.

Whether you dive in to USB 3.0 as soon as you can or wait until there are plenty of devices out there than can take advantage of it, the move from USB 2.0 to USB 3.0 should be as smooth as upgrading from USB 1.1 was.

But USB 3.0 is something of a departure from 2.0 from both technical and practical standpoints, and while the minds behind the new standard have made backward compatibility a cornerstone of their development efforts, USB 3.0 is not simply a higher-clocked USB 2.0.

USB 3.0's raison d'etre is to up data-transfer rates to ten times what USB 2.0 can manage, jumping from 480Mb/s to 5Gb/s, needed now we're throwing HD video files around. Error handling and the needs of the data-transfer protocol will reduce that some, just as it does with 2.0, but the new bus nonetheless justifies its 'SuperSpeed' moniker.

What goes into USB 3.0

Achieving that data rate has required some hardware changes. Skinny, unshielded cabling that's fine for USB 2.0 is out, replaced by shielded, multi-core wires-within-wires - Shielded Differential Pair, or SDP - cables, which will be thicker than those we're used to. Shielding is needed to cut out the electromagnetic interference that reduce the signal integrity and prevent the bus from achieving that 5Gb/s throughput. You simply can't do SuperSpeed over USB 2.0 cabling.

Adaptive equalisation circuitry in each device helps it all along. AE allows the state of the connection to be measured and the electrical signal altered to optimise data delivery over that particular physical connection, compensating for differing lengths of cable and different quality wiring.